Japanese quail eggs were subjected to 2.45 GHz CW microwave radiation at 5\mW/cm squared (SAR = 4.03 mWg) during the first 12 days of embryogeny and reared to 22 weeks of age before examination. Humoral immune potential, as indicated by comparable anti-CRBC antibody, IgM and IgG, levels at 0, 4 and 7 days post-immunization in both exposed and control quail, was not affected significantly. However, cell mediated immune potential measured by the reaction to intradermal injection of phytohemagglutinin-P in the wing web, was reduced in the exposed females, but not in the exposed males. Additionally, total leucocyte numbers and absolute circulating numbers of lymphocytes, monocytes and heterophils were increased significantly only in the exposed females. Studies to determine the effects of microwave exposure as indicated above on brain development showed a slight development retardation in the cerebellar cortices. In fertility studies in adult Japanese quail exposed during embryogeny a decrease in spermatozoal numbers and motility were measured in exposed males and a decrease in fertility of approximately 10 percent occurred in eggs from mating of exposed male with either exposed or control females.